Data that show correlations of peripheral blood thymus dependent lymphocyte (T cell) levels as determined by in vitro E rosette formation and in vivo cell-mediated immunity give importance to the development of objective means of determining T cell levels. We have developed a technique for determining T cell levels by cytofluorographic analysis utilizing glutaraldehyde fixation of the lymphocytes that correlates with levels determined by light-microscope counting. Cytofluorographic display of lymphocytes from patients receiving radiation therapy and chemotherapy show patterns differing from normals or untreated cancer patients. Studies are in progress to determine the functional classification of these lymphocyte subpopulations and their correlation with clinical course and response to therapy. Recent studies demonstrate that cyclic nucleotide levels in human peripheral blood lymphocytes parallel T cell levels. Preliminary studies in our laboratory confirm this correlation. Studies in progress are designed to determine the usefulness of this assay as a correlate of cellular immunity and the host-tumor relationship. Particular emphasis will be placed on correlations of lymphocyte cyclic nucleotide levels and response to therapy in cancer patients. BIBLIOGRAPHIC REFERENCES: Silverman, N.A., Alexander, J.C., Jr., Hollinshead, A.C., and Chretien, P.B.: Correlation of tumor burden with in vitro lymphocyte reactivity and antibodies to herpesvirus tumor-associated antigens in head and neck squamous carcinoma. Cancer 37:135-140 1976. Tarpley, J.L., Twomey, P.L., Catalona, W.J., and Chretien, P.B.: Suppression of cellular immunity by anesthesia and operation. J. Surg. Res. 22:195-201, 1977.